Gastrointestinal (GI) mucosal injury from insults such as ethanol, bile, and aspirin continues to be a major health care problem, often-necessitating hospitalizations, and occasionally surgery. The underlying difficulty in managing this disorder relates to our current lack of understanding regarding the precise mechanism(s) responsible for its pathogenesis. A considerable body of knowledge indicates that prostaglandins (PGs) have the amazing capability to markedly reduce the magnitude of GI damage histologically when induced under a wide variety of experimental circumstances. During the present funding period, we observed that damaging agents appear to mediate their injurious effects through a common mechanism, namely alterations in intracellular calcium accumulation that results in cytoskeletal disruption and ultimate cell death. We further observed that PG pretreatment can prevent these perturbations concomitant with its protective action through activation of protein kinase C that thereby restores calcium homeostasis via activation of calcium extrusion from cells. The protective action of growth factors (i.e. EGF and TGF alpha) against gut damaging agents appears to be mediated through a similar mechanism. Based on these observations, we believe that maintenance of cellular cytoskeletal integrity through intracellular calcium stabilization may be a fundamental mechanism by which PGs (and other protective agents) mediate their cellular protective action, and provides a unifying hypothesis to explain the underpinnings of GI injury and protection. To validate this hypothesis, our specific aims during this new grant period will be (1) to determine whether damaging substances induce apoptosis in gastric and intestinal cells and whether PGs and other protective agents initiate protection through prevention of this process, (2) to elucidate the role of protein kinase C in GI cellular injury and protection, and (3) to define more precisely the relationship between intracellular calcium homeostasis, cytoskeletal stability and GI cellular injury.